While it is known that pharmaceuticals enter aquatic ecosystems as pollution, little has been known about their effects on wildlife. Now, there is some disturbing news from studies of fish. Tomas Brodin and colleagues at the University of Umeå in Sweden subjected wild European perch (Perca fluviatilis) to oxazepam – a benzodiazepine anxiolytic drug used to treat anxiety – at levels of 1.7 μg/l. Fish from the Fyris river had been found in the wild to have six times the concentration as the surrounding water (0.58 μg/l), indicating that the drug concentrates in the fish, so the dose seemed a fair one for a quick test.

After seven days, the fish had levels similar to what they received in the wild. The perch, which are normally shy and hunt together, showed increased activity, reduced sociability and higher feeding rates. This is just one drug of a vast cocktail that is now found in natural water sources, so there is clear cause for concern.